Blood transfusion has been a major option for the treatment of diseases such as sickle cell anemia and thalassemia. Surgery and trauma conditions also often require blood transfusion. In most of the cases a match between patient and donor blood is made by testing for major group antigens ABO and RhD. However, patients receiving blood transfusion repeatedly develop alloimmunization against non-ABO/RhD antigens (e.g., Castro et al., 2002). Eventually, it becomes very difficult to find a perfect donor for such patients. This problem is more prominent for sickle cell patients who are usually of African origin while the donors are usually whites (e.g., Issitt, 1994). The difference in the Rh antigens between these two communities is a major concern about allosensitization in sickle cell patients.
Attempts have been made to generate universal erythrocytes to overcome difficulties such as those mentioned above. Universal erythrocytes are needed especially for trauma conditions where there is no time to perform tests for blood group matching. Enzymatic digestion has been used to remove antigen specific carbohydrates from the membrane of red blood cells (RBCs) (Goldstein et al., 1982). B group RBCs have been converted to O group RBCs by enzymatic cleavage of the B group specific antigen, galactose. These RBCs have been successfully transfused into O group individuals (Lenny et al., 1994, 1995). However, this strategy requires the use of different enzymes to remove different types of antigens. Moreover, this protocol cannot be used for protein antigens such as the Rh system since these proteins are closely associated with the cell membrane (Avent and Reid, 2000).
Masking antigens by attaching bulky polymer chains to the surface of RBCs has been used as another approach to develop universal RBCs. Functionalized polyethylene glycol (PEG) chains have been used to modify RBC membrane proteins (Bradley et al., 2002; Jeong and Byun, 1996; Scott et al., 1997; U.S. Pat. No. 6,312,685). These PEG chains by being hydrophilic become heavily hydrated and can cover a large surface area of the RBC membrane and thus can prevent the accessibility of the blood group antigens to antibodies. PEG-cyanuric chloride is the most common reagent used for pegylation of erythrocytes (Blackall et al., 2001; Bradley et al., 2001, 2002; Jeong and Byun, 1996; Sabolovic et al., 2000; Scott et al., 1997; U.S. Pat. No. 6,312,685). This functionalized PEG reagent modifies mostly amino groups on proteins (Roberts et al., 2002). Pegylation of RBCs with PEG-5000 activated with cyanuric chloride has been reported to mask Rh antigens to a reasonable extent. In contrast, A or B antigens were only partially masked by this procedure (Bradley et al., 2001; Jeong and Byun, 1996; Scott et al., 1997; U.S. Pat. No. 6,312,685). Masking of the A and B antigens of RBCs is critical for developing universal red blood cells.